In a Long Term Evolution (Long Term Evolution, LTE) system, cross-site carrier aggregation may exist in the future, that is, multiple different sites are configured for one terminal, so as to increase a throughput of the terminal and simplify terminal mobility management.
In a case of cross-site carrier aggregation, a receive end at a Radio Link Control (Radio Link Control, RLC) layer, a Packet Data Convergence Protocol (Packet Data Convergence Protocol, PDCP) layer, or an Internet Protocol (Internet Protocol, IP) layer of an air interface may receive multiple data streams of one radio bearer (Radio Bearer, RB for short). These data streams come from a multi-stream aggregation (Multiple-stream Aggregation, MSA for short) site.
Because load statuses and radio channel conditions of different sites are different, the multiple data streams of one radio bearer may experience different transmission delays, namely, non-uniform transmission delays. For transmission in an unacknowledged mode (Un-acknowledgement Mode, UM), if multi-stream data is aggregated at the RLC layer, the receive end needs to maintain a reordering window (Reordering Window) to perform, according to a sequence number of the RLC layer, reordering on data delivered from a medium access control (Medium Access Control, MAC) layer, so as to implement sequential delivery to the PDCP layer. A size of the reordering window is generally half of a range represented by a sequence number (Sequence Number, SN). For example, if the SN is formed by 10 bits, the size of the reordering window is 512 (that is, half of 2 to the power of 10). How to ensure normal communication between a terminal and a base station in a multi-stream aggregation scenario has become a problem that needs to be resolved urgently in the industry.